The present invention relates to nitro dyes for dyeing hair and, more specifically, to 2,6-dinitro-aniline derivatives used as nitro dyes, as well as to the use of compositions containing 2,6-dinitro-aniline derivatives and to the novel 2.6-dinitro-aniline derivatives.
The use of nitro dyes in hair dyes is widespread today. They are used in oxidation hair dyes as additives for producing natural or modern shades. However, by combining several differently colored nitro dyes it is also possible to produce hair dyes which are capable of dyeing hair in natural to modern shades without the use of oxidizing agents.
Thus, brown colours having a natural effect can be produced by combining, for example, an orange-dyeing nitro dye with a blue-dyeing one. However, in addition, it is also possible to obtain a similar result with a yellow-dyeing and a violet-dyeing nitro dye. Therefore, either yellow nitro dyes which can dye the hair in an intense pure lemon-yellow colour, that must be as free from red components as possible, or those which dye the hair orange and can be applied in combination with pure blue dyes are required.
Furthermore, hair dyes must satisfy many additional requirements. The nitro dyes must be harmless in toxicological and dermatological respects. For their use in oxidation dyes it is a prerequisite that they are stable in the presence of hydrogen peroxide in alkaline solution. Furthermore, a good light fastness, resistance to acid and rubbing fastness are required for the hair colorations produced. Finally, it should be possible to produce the nitro dyes by a simple process.
The substituted amino-nitrophenols described in their literature heretofore for dyeing the hair yellow satisfy the above-mentioned requirements only to a limited extent. It is true, the 4-nitro-3-(2'-hydroxy-ethyl)aminophenol described in International Journal of Cosmetic Science 1982, Page 25 to 35, does produce a lemon-yellow coloration. However, this coloration has a very low color intensity. Two further isomers, namely, the 4-nitro and the 5-nitro-2(2'-hydroxy-ethyl)aminophenol are pH-sensitive due to the aromatic hydroxy groups and show undesirable colour changes when exposed to the action of acid or alkali.
The o-, m- and p-nitro-aniline derivatives mentioned in DE-AS 1619395 are further known nitro dyes. In fact these compounds substantially satisfy the requirements with regard to the application technology but they are not satisfactory with regard to physiological properties.
The 2-nitro-aniline derivatives described in DE-OS 3 442 757 do satisfy the requirements to a great extent but the color scale attainable by varying the substituents cannot be extended into the red range. Therefore, no modern reddish hair colors can be produced with the 2-nitro-aniline derivatives described therein without the additional application of red dyes.